1. Field of the Invention
The present invention relates to polymer nanocomposites of layer structured inorganic/polyelectrolyte/organic polymer, and a method of preparing the same.
2. Description of the Prior Art
Nanocomposites are the composites that the diameter of its dispersed particles are in the range of 1-100 nm. In particular, the nanocomposites contain layered inorganic material, such as clay, which has the characteristics of nanoscale layer thickness, a high aspect ratio, and ionic bonding between layers. As a result, the material has high strength, high rigidity, high resistance to heat, low moisture absorption, low gas permeability and can be multiple recycled for reuse. The currently available commercial product of this nano-composites material is Nylon 6/clay from Ube Company, Japan, which is used in vehicle parts and air-blocking wrapping films (1990); and from Unitika Company, Japan, which is used in vehicle parts and as an engineering plastic (1996).
Conventional methods to produce nanocomposites are: (1) in-situ polymerization, (2) kneading and (3) coagulation and sedimentation. Nylon 6 nanocomposite has been successfully commercialized by in-situ polymerization. However, this method is successful for Nylon 6 nanocomposites only until to now. Moreover, although kneading is convenient, the equipment is considerably expensive and the relative techniques are very complex. It has not been commercialized.
As for coagulation and sedimentation, most research, such as Applied Clay Science volume 15 (1999), pages 1xcx9c9, has shown that it is hard to avoid the re-coagulate of the layered inorganic material. For example, the preparation methods of nanocomposite of Styrene-Butadiene Rubber (SBR) as disclosed in the journal of Special Rubber Products, issued by Beijing-Univ-Chem-Technol in China, volume 19 (2), pages 6xcx9c9, 1997, include:
(1) Latex method: Vigorously stirring the aqueous to allow clay dispersed in water, SBR latex and antioxidant are then added and uniformly mixed. The mixture is coagulated with the addition of diluted hydrochloric acid. After it is washed with water and dried, clay/SBR nanocomposite is obtained. The lattice spacing of the clay is expanded from 0.98 nm of pure clay to 1.46 nm. This indicates that SBR molecules inserted between layers of clay to form intercalated nanocomposites.
(2) Solution method: Modify the clay by organic chemicals and the obtained clay is vigorously stirred to disperse in toluene. A SBR-toluene solution is then added and the mixture is stirred vigorously to become a uniform mixture. After it is sedimented and dried, clay/SBR nanocomposite is obtained. The lattice spacing of clay is expanded from 0.98 nm of pure clay to 1.90 nm after it is organically modified, and further expanded from 1.90 nm to 4.16 nm in clay/SBR nanocomposite. This indicates that more SBR molecules are inserted into layers of clay than the above latex method. Nevertheless, this method uses a large amount of toluene, which causes the production cost to increase and the occurrence of environmental problems.
From the above, it is found that the biggest breakthrough for coagulation and sedimentation is how to easily and effectively prevent the coagulation of layered inorganic material itself. This invention solves the problem by using polyelectrolytes with multiple charges to prevent the coagulation of layered inorganic material. At the same time, the polyelectrolytes are used as coagulant between layered inorganic material and polymer latex.
The first object of the invention is to provide a easy xe2x80x9ccoagulationxe2x80x9d method to produce polymer nanocomposites.
The second object of the invention is to provide a method to produce polymer nanocomposites in aqueous and/or including the addition of small amounts of organic solvents.
The third object of the invention is to prepare a polylmer nanocomposite containing polyelectrolyte.
The fourth object of the invention is to provide the preparation of a layered inorganic material/polyelectrolyte/polymer latex nanocomposites and the method of preparing the same. In the invention, the used polyelectrolyte contains opposite charges relative to that of the layered inorganic material and the polymer latex.
To achieve the above-mentioned objects, the invention introduces polyelectrolytes to the solution of the layered inorganic material, such as a clay solution, and a polymer latex. The clay is fully dispersed in water, and the polyelectrolyte with opposite charges to clay is then added to form a complex through the combination of the relative opposite charges in clay and polyelectrolyte. Extra charges of the polyelectrolyte of the complex will combine again with the surface charges of the polymer latex. By way of these coagulations, a well-dispersed nanocomposite of layered inorganic material/polyelectrolyte/polymer latex is formed.
In more detail, the method of preparing polymer nanocomposites of the invention comprises the following steps: (a) combining layered inorganic material, such as clay, and polyelectrolyte in a water solution to form a complex, wherein the polyelectrolyte contains extra amount of opposite charges relative to the clay, and this charge combination will adsorb the polyelectrolyte onto the clay; and (b) adding the complex in (a) to a polymer latex, wherein the polymer latex contains opposite charges relative to the polyelectrolyte, and by way of cogulation, a composite of layered inorganic material/polyelectrolyte/polymer latex is formed.
The polymer nanocomposites of the invention comprise of (a) high molecular polymer as a matrix; (b) layered inorganic material, which is dispersed in the matrix of high molecular polymer; and (c) polyelectrolyte, which contains opposite charges relative to the layered inorganic material and is adsorbed onto the layered inorganic material.
Compared to the prior art, the characteristics of the invention include:
(1). In comparison to the latex method mentioned in the journals, the introduction of polyelectrolyte in the invention leads to a coagulation process, wherein the opposite charges carried by polyelectrolyte relative to the clay and polymer latex results in the combination of the clay, the polymer latex and the polyelectrolytes. As a result, the method to obtain nanocomposites do not need additional equipment and other cost except the polyelectrolytes.
(2). In comparison to the solution method, this invention avoids the use of large amounts of organic solvents.